The teenage boy walking in the southbound curb lane of the U.S. 31 bridge was neither hitchhiking, nor was he dressed for a Saturday afternoon swim.

So when he hunched over and dropped about 50 feet to the Tennessee River, diners at the nearby Hard Dock Café were dumbfounded.

"I said, 'I guess he's going to jump,' but I was just kidding. I didn't think he actually would," witness Bobby Matthews said of boy wearing a ball cap, a T-shirt, shorts and sneakers. Matthews guessed he was 15 years old.

But the Huntsville resident, who was sitting on the restaurant's deck, wasn't surprised when the boy resurfaced swimming to a waiting boat. If the boy was trying to injure himself, Matthews noted, he would have most likely jumped from a higher spot, closer to the center of Hudson Memorial Bridge.

Matthews and friend Sheila Brady realized they were among several spectators to a stunt, including six or seven teenage boys in a maroon and white getaway speedboat, one stationed in a yellow and brown kayak, and another positioned on dock to take pictures.

"I didn't realize I was going to get free entertainment," Matthews joked.

The photographer and kayaker slipped away soon after first responders were dispatched to reports of a possible drowning. The boat, tailed by Alabama Marine Police, sped west.

A half-hour after the 3:30 p.m. incident, the patrol vessel had given up chase and returned to the harbor. The last rescue worker, Decatur fire Lt. Daryl Jones, was preparing to leave.

Jones said the prank was just the latest of several recent reports of thrill-seeking jumps.